Two prior art tools are known to applicant that comprise a flexible device for removing deposits from the exterior surfaces of pipes. These are disclosed in U.S. Pat. No. 1,283,070 issued to Callender on Oct. 29, 1918, and U.S. Pat. No. 3,214,824 issued to Brown on Nov. 2, 1965. Each of these prior art devices has shortcomings that have meant that they are not in use today, so far as applicant is aware, by those who repair underground pipe installations, usually after a break in the pipe.
The Callender device presents widely spaced cutting edges against the exterior surface of the pipe being cleaned, and thus is highly inefficient. Second, because of the rotatable mounting of its cutters or bits, the Callender device is likely to ride over (rather than remove) difficult obstructions on the exterior surface of the pipe being cleaned. Third, it is likely to become clogged with the scale and other debris that are removed from any heavily encrusted pipe.
The Brown patent was issued 47 years after the Callender patent. However, rather than solving the first two shortcomings of the Callender tool, it actually moved farther away from any such solution by exaggerating the same shortcomings. As to the third problem of clogging, because of its particular knurled scraper members it merely exchanged one type of clogging for another.
Apparently as a result of the shortcomings of the two prior art devices under discussion, so far as applicant is aware the only tool that is currently used to clean the surface of a pipe in a preexisting underground installation is a flat bar scraper. Since such pipes are usually installed at a depth of about three to five feet below the surface of the ground, it is necessary to climb down into the excavation, or hang over the pipe while attempting to scrape the bottom of the pipe. In addition to being very difficult, this process is very slow.
Use of the pipe scraping tool of the present invention avoids the shortcomings just discussed. This makes possible cost savings of as much as 50 percent for municipalities and utility companies who are required to repair broken pipes in underground install- ations.